/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.socket.sockjs.transport.handler;

import java.io.IOException;
import java.nio.charset.StandardCharsets;
import java.util.Map;

import org.springframework.http.HttpStatus;
import org.springframework.http.MediaType;
import org.springframework.http.server.ServerHttpRequest;
import org.springframework.http.server.ServerHttpResponse;
import org.springframework.util.StringUtils;
import org.springframework.web.socket.CloseStatus;
import org.springframework.web.socket.WebSocketHandler;
import org.springframework.web.socket.sockjs.SockJsException;
import org.springframework.web.socket.sockjs.SockJsTransportFailureException;
import org.springframework.web.socket.sockjs.frame.DefaultSockJsFrameFormat;
import org.springframework.web.socket.sockjs.frame.SockJsFrameFormat;
import org.springframework.web.socket.sockjs.transport.SockJsServiceConfig;
import org.springframework.web.socket.sockjs.transport.SockJsSession;
import org.springframework.web.socket.sockjs.transport.TransportHandler;
import org.springframework.web.socket.sockjs.transport.TransportType;
import org.springframework.web.socket.sockjs.transport.session.AbstractHttpSockJsSession;
import org.springframework.web.socket.sockjs.transport.session.StreamingSockJsSession;
import org.springframework.web.util.JavaScriptUtils;

/**
 * An HTTP {@link TransportHandler} that uses a famous browser document.domain technique:
 * <a href="http://stackoverflow.com/questions/1481251/what-does-document-domain-document-domain-do">
 * http://stackoverflow.com/questions/1481251/what-does-document-domain-document-domain-do</a>
 *
 * @author Rossen Stoyanchev
 * @since 4.0
 */
public class HtmlFileTransportHandler extends AbstractHttpSendingTransportHandler {

    private static final String PARTIAL_HTML_CONTENT;

    // Safari needs at least 1024 bytes to parse the website.
    // http://code.google.com/p/browsersec/wiki/Part2#Survey_of_content_sniffing_behaviors
    private static final int MINIMUM_PARTIAL_HTML_CONTENT_LENGTH = 1024;


    static {
        StringBuilder sb = new StringBuilder(
                "<!doctype html>\n" +
                        "<html><head>\n" +
                        "  <meta http-equiv=\"X-UA-Compatible\" content=\"IE=edge\" />\n" +
                        "  <meta http-equiv=\"Content-Type\" content=\"text/html; charset=UTF-8\" />\n" +
                        "</head><body><h2>Don't panic!</h2>\n" +
                        "  <script>\n" +
                        "    document.domain = document.domain;\n" +
                        "    var c = parent.%s;\n" +
                        "    c.start();\n" +
                        "    function p(d) {c.message(d);};\n" +
                        "    window.onload = function() {c.stop();};\n" +
                        "  </script>"
        );

        while (sb.length() < MINIMUM_PARTIAL_HTML_CONTENT_LENGTH) {
            sb.append(" ");
        }
        PARTIAL_HTML_CONTENT = sb.toString();
    }


    @Override
    public TransportType getTransportType() {
        return TransportType.HTML_FILE;
    }

    @Override
    protected MediaType getContentType() {
        return new MediaType("text", "html", StandardCharsets.UTF_8);
    }

    @Override
    public boolean checkSessionType(SockJsSession session) {
        return session instanceof HtmlFileStreamingSockJsSession;
    }

    @Override
    public StreamingSockJsSession createSession(
            String sessionId, WebSocketHandler handler, Map<String, Object> attributes) {

        return new HtmlFileStreamingSockJsSession(sessionId, getServiceConfig(), handler, attributes);
    }

    @Override
    public void handleRequestInternal(ServerHttpRequest request, ServerHttpResponse response,
            AbstractHttpSockJsSession sockJsSession) throws SockJsException {

        String callback = getCallbackParam(request);
        if (!StringUtils.hasText(callback)) {
            response.setStatusCode(HttpStatus.INTERNAL_SERVER_ERROR);
            try {
                response.getBody().write("\"callback\" parameter required".getBytes(StandardCharsets.UTF_8));
            } catch (IOException ex) {
                sockJsSession.tryCloseWithSockJsTransportError(ex, CloseStatus.SERVER_ERROR);
                throw new SockJsTransportFailureException("Failed to write to response", sockJsSession.getId(), ex);
            }
            return;
        }

        super.handleRequestInternal(request, response, sockJsSession);
    }

    @Override
    protected SockJsFrameFormat getFrameFormat(ServerHttpRequest request) {
        return new DefaultSockJsFrameFormat("<script>\np(\"%s\");\n</script>\r\n") {
            @Override
            protected String preProcessContent(String content) {
                return JavaScriptUtils.javaScriptEscape(content);
            }
        };
    }


    private class HtmlFileStreamingSockJsSession extends StreamingSockJsSession {

        public HtmlFileStreamingSockJsSession(String sessionId, SockJsServiceConfig config,
                WebSocketHandler wsHandler, Map<String, Object> attributes) {

            super(sessionId, config, wsHandler, attributes);
        }

        @Override
        protected byte[] getPrelude(ServerHttpRequest request) {
            // We already validated the parameter above...
            String callback = getCallbackParam(request);
            String html = String.format(PARTIAL_HTML_CONTENT, callback);
            return html.getBytes(StandardCharsets.UTF_8);
        }
    }

}
